Acetonitrile Synthesis via Ammoxidation: Mo/zeolites Catalysts Screening

Abstract

Mo/zeolites catalysts were investigated in ethane and ethylene ammoxidation into acetonitrile. The catalysts were prepared either in solid‒solid or liquid‒solid interface after varying different parameters. The stabilization of Mo species upon the exchange is dependent on the hydrophilic/hydrophobic character of the zeolite and the type of Mo precursor. In fact, zeolites with low Si/Al molar ratios should be avoided due to their higher dehydration enthalpy values (Δ_dehyd.H). On the other hand, the use of MoOCl₄, Mo(CO)₆ and MoCl₃ precursors and zeolites with high Si/Al ratios led to inefficient [Mo₇O₂₄]^6‒ species and amorphous MoO₃ which catalyzes the combustion reaction. Nevertheless, the use of MoCl₅, MoO₃ and MoO₂(C₅H₇O₂)₂ led to promising activities. In catalysis, [MoO₄]^2‒ species are required to activate C₂H₆ into C₂H₄, while [Mo_xO_3x+1]^2‒ (x =1, 2) species catalyze the ammoniation of C₂H₄ and the ethylamine dehydrogenation into CH₃CN. Interestingly, active catalysts could be obtained by humid impregnation and a simultaneous oxidative treatment. Such a treatment improves the dispersion state of crystalline MoO₃, which activate ethane molecules. It is judicious to perform C₂H₆ oxidative dehydrogenation before ammoxidation since the interference between the different investigated parameters could be noted.